1. Field of the Invention
The invention relates generally to an improved hydrocyclone liner composed of a combination of materials, especially liquid-liquid liners used for petroleum fluid processing.
2. Description of the Related Art
The overall construction and manner of operation of hydrocyclone liners is well known. A typical hydrocyclone liner, also referred to as merely a “hydrocyclone,” includes an elongated body surrounding a tapered separation chamber of circular cross-section, which separation chamber decreases in cross-sectional size from a large overflow and input end to a narrow underflow end. An overflow or reject outlet for the lighter fraction is provided at the wider end of the conical chamber while the heavier underflow or accept fraction of the suspension exits through an axially arranged underflow outlet at the opposite end of the conical chamber. Liquids and suspended particles are introduced into the chamber via one or more tangentially directed inlets, which inlets create a fluid vortex in the separation chamber. The centrifugal forces created by this vortex throw denser fluids and particles in suspension outwardly toward the wall of the conical separation chamber, thus giving a concentration of denser fluids and particles adjacent thereto, while the less dense fluids are brought toward the center of the chamber and are carried along by an inwardly-located helical stream created by differential forces. The lighter fractions are thus carried outwardly through the overflow outlet. The heavier particles continue to spiral along the interior wall of the hydrocyclone liner and exit the liner via the underflow outlet.
The fluid velocities within a hydrocyclone liner are high enough that the dynamic forces produced therein are sufficiently high to overcome the effect of any gravitational forces on the performance of the device. Hydrocyclone liners may, therefore, be arranged in various physical orientations without affecting performance. Hydrocyclone liners, especially those for petroleum fluid processing, are commonly arranged in large banks of several dozen or even several hundred hydrocyclone liners with suitable intake, overflow and underflow assemblies arranged for communication with the intake, overflow and underflow openings, respectively, of the hydrocyclone liners.
Hydrocyclone liners are used both for the separation of liquids from solids in a liquid/solid mixture (“liquid/solid hydrocyclones”) as well as for the separation of liquids from other liquids (“liquid/liquid hydrocyclones”). Different constructions are used for each of these hydrocyclone devices. The liquid/liquid type of hydrocyclone liner is longer in the axial direction than a solid/liquid hydrocyclone liner and is thinner as well. As a result of these structural differences, the engineering of a liquid/liquid hydrocyclone liner that is both erosion-resistant and which can support its own weight is challenging.
It is noted that erosion resistance has heretofore not been considered as important a design consideration for liquid/liquid hydrocyclone liners as for liquid/solid hydrocyclone liners, since liquid/solid hydrocyclones have been expected to experience greater wear due to the large amount of solids present in the material being separated. Liquid/liquid hydrocyclones, by contrast, are considered to have no or very little solids content and, therefore, erosion is less of a concern. Conventionally, then, liquid/liquid hydrocyclone liners have been designed for optimal corrosion resistance, assuming either no or very little erosion, and then later discarded or repaired in the event of erosion damage to the liners. In fact, however, erosion of liquid/liquid hydrocyclones is a serious problem in certain installations. Impurities in the form of solid particles are suspended in the liquids to be separated. The inventors have recognized that these solid particles are capable of causing tremendous erosion of the hydrocyclone liner, particularly upon those portions of the liner that experience high rotational fluid forces. Thus, an improved erosion-resistant liquid/liquid hydrocyclone liner would be desirable.
Normally, hydrocyclone liners for separating fluids are made from one or more homogeneous materials. When increased resistance to erosion is required (due to entrained solids in the fluids), the current practice is to simply substitute the original material of the liner for an erosion-resistant material, such as alumina ceramic or tungsten carbide. If the diameter of the hydrocyclone liner is large enough, such as for solid-liquid separating liners, it may be possible to spray an erosion-resistant coating into the bore of the liner. Repeated spraying of such coating allows a longer life for the liner. This is not generally an available option for narrow bore liquid/liquid liners, such as is used in petroleum fluid processing. Access to the interior surfaces of the liner is limited due to the small diameter (typically less than 2″) of portions of the liner, and the length of the liner makes an even and complete coating unlikely. Further, only a limited number of suitable coating treatments are known that will harden the steel of the liner against erosion without compromising its corrosion resistant properties.
Erosion-resistant materials, such as ceramics or certain alloys, may be very heavy or brittle, such that the construction of the entire liner from such erosion-resistant material is not desirable. For example, tungsten carbide, a common erosion-resistant material, is twice as dense as steel. A hydrocyclone liner comprised entirely of an erosion-resistant material, such as tungsten carbide, might not be fit for service due to poor mechanical properties (including weight and tensile strength) and high cost. Liquid/liquid hydrocyclone liners are typically installed horizontally, being supported by a support plate at either end. Depending on the mode of installation, the liners may be left cantilevered from one support plate, with the liner having to take the weight of the head casting, while the second support plate is moved into position. Also, installation may require that a liner be physically hammered into place in the first support plate. During installation, then, a heavy and brittle liner might easily be damaged. As petroleum fluid processing is often located in shipboard installations or on off-shore platforms, a highly reliable and relatively lightweight hydrocyclone liner is desired.
A few designs are known for erosion-resistant hydrocyclones and hydrocyclone liners. For one reason or another, however, these prior art designs are unsatisfactory and/or do not provide an acceptable design for an erosion resistant liquid/liquid hydrocyclone liner.
U.S. Pat. No. 4,053,393 issued to Day et al., for example, describes a cyclone assembly for separation of fluids of different densities that includes an erosion-resistant insert body that is disposed within the diametrically smaller end of the hydrocyclone liner body. This liner body, according to Day et al., is formed of a synthetic plastic material, while the insert body may be formed of various metals, ceramics, synthetic materials of various hardness's, or natural and synthetic elastomers. The insert body is retained within the liner body by a series of annular shoulders that interlock with complimentary shoulders on the liner body.
The Day et al. design does not provide adequate erosion protection for the inner surfaces associated with the inlet portion of the hydrocyclone because the erosion protection is only provided at and around the reduced diameter portion of the hydrocyclone. However, the velocity of particles entering the hydrocyclone at the inlet portion does result in significant erosion at and near the inlet portion. Day et al.'s design does nothing to prevent or slow this erosion.
U.S. Pat. No. 4,539,105 issued to Metcalf illustrates a cyclone separator that includes an outer plastic sleeve that houses an interior separator cone made of abrasion resistant material, that may include metal, such as stainless steel, or ceramic material, such as aluminum oxide ceramic material, or silicone carbide ceramic.
Metcalf's liner design is intended for, and indeed only suitable for, solid/liquid hydrocyclones. Specifically, the design is intended for use where the mixture entering the hydrocyclone contains a heavy fractional material, such as solid particles of sand, or pulp stone grit of aluminum oxide or silicon carbide, such as when the stock is a solution of paper pulp formed by pulp stone grinding. As noted, a liquid/liquid hydrocyclone is configured differently from a solid/liquid hydrocyclone, such as that described in the Metcalf patent, at least in that the wider, inlet end and tapered portion of a liquid/liquid hydrocyclone is much narrower and longer than the inlet end and tapered portions of the solid/liquid hydrocyclone. For example, the wider end of a solid/liquid hydrocyclone is typically about 1500 mm in diameter, as compared with 20–40 mm for a liquid/liquid hydrocyclone. This difference in dimensions ensures that Metcalf's design is unsuitable for liquid/liquid hydrocyclones. The weight and strengths of the materials involved make it unlikely that a narrower liquid/liquid hydrocyclone, constructed using Metcalf's described configuration, would be able to support its own weight and be robust enough to have a very long operational life.
It is desired to have a hydrocyclone liner for liquid-liquid separation, which liner is capable of withstanding the erosive effects of particles trapped within the liquids being separated.
It is further desired to have an erosion-resistant hydrocyclone liner that does not have significantly poorer physical characteristics than non-erosion-resistant liners. It is also desired to have a hydrocyclone liner that provides improved erosion-resistant characteristics for those specific portions of the liner that experience the greatest degree of erosion during use.
There is a need to provide improved methods and devices for resisting erosion of, and thereby extending the service life of, hydrocyclone liners. The present invention addresses the problems of the prior art.